Shaping Magnetite with Poly-l-arginine and pH: From Small Single Crystals to Large Mesocrystals

Abstract

Control over particle size, size distribution, and colloidal stability are central aims in producing functional nanomaterials. Recently, biomimetic approaches have been successfully used to enhance control over properties in the synthesis of those materials. Magnetotactic bacteria produce protein-stabilized magnetite away from its thermodynamic equilibrium structure. Mimicking the bacteria’s proteins using poly-l-arginine we show that by simply increasing the pH, the dimensions of magnetite increase and a single- to mesocrystal transformation is induced. Using synchrotron X-ray diffraction and transmission electron microscopy, we show that magnetite nanoparticles with narrow size distributions and average diameters of 10 ± 2 nm for pH 9, 20 ± 2 nm for pH 10, and up to 40 ± 4 nm for pH 11 can be synthesized. We thus selectively produce superparamagnetic and stable single-domain particles merely by controlling the pH. Remarkably, while an increase in pH brings about a thermodynamically driven decrease in size for magnetite without additives, this dependency on pH is inverted when poly-l-arginine is present.

Wettability of Magnetite Nanoparticles Guides Growth from Stabilized Amorphous Ferrihydrite

“…The addition of poly(arginine) shifts the reaction control from thermodynamic to kinetic, directing nanoparticle growth via precursor attachment reactions and explaining the elusive inversion of the magnetite size dependence on pH. 17 The unexpected wetting of the liquidlike precursor and the consecutive homoepitaxial crystallization induce single-crystalline properties. These properties are even observed within the substructured, discontinuous nanoparticles obtained at high pH, which—not complying to the classification of a mesocrystal 36 —can be regarded as semicontinuous single crystals.…”

“… 16 A better understanding of these contributions will enable us to engineer organic/inorganic hybrid systems as well as purely crystalline nanoscopic systems. However, because of low concentration, 17 low density, and strong hydration of the involved amorphous precursors, temporally and structurally resolving their involvement in crystallization pathways in their native environment to infer a mechanism remains challenging.…”

Biomineralization of Magnetosomes: Billion-Year Evolution Shaping Modern Nanotools

“…Poly-arginine also improves the tuneability of the biomimetic synthesis. In the presence of the additive, the average diameters of the magnetite precipitates could be adjusted from 10 to 40 nm when the reaction occurred in pHs from 9 to 11, respectively [94].…”

Fe3O4 Mesocrystals with Distinctive Magnetothermal and Nanoenzyme Activity Enabling Self-Reinforcing Synergistic Cancer Therapy

“…Fan et al , synthesized Cu 2 O nanowire MCs with high POD activity because of the large surface area and uniform channel structure and demonstrated their promising wastewater bioremediation. Fe 3 O 4 MCs, as one of the most important inorganic MCs, have been widely studied for their preparation methods and formation mechanism, and generally, it is believed that the performance of Fe 3 O 4 MCs relies to a great extent on its crystallinity, surface nature, microstructures, and so forth. − It would be exciting to expect multifunctional Fe 3 O 4 MCs to be used in the new treatment method of tumor therapy.…”